Radiofrequency amplifying circuits



Nov. 20, 1928.

w. J. POLYDROF'F RADIO FREQUENCY I AMPLIFYING CIRCUITS Filed Feb. 5, 1927 U W w I Y E+ Q N w R.. IHWW nuluun m N S m a: @MQ ww n .MWL l 4 TJ MW A .ru #u V 'WL/mmm@ PoLYDoRoFF, BY

Patented Nev. 20,1928.

UNITED sTATEs 1,692,763 PATENT OFFICE. l j

WLADIMIR J. POLYDOBOFFQOF CHICAGO, ILLINOIS, ASSIGNOR TO JOHNSON-WILLIAM- SON' LABORATORIES, INC., OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

BADIOFREQUENCY AMPLIFYING CIRCUITS.

Application tiled February 5, 1927. Serial No. 166,107.

The invention relates to radio-frequency amplifying circuits wherein three-electrode tubes are used as amplifiers, and, generically considered, consists of means for preventing undesirable oscillations in said circuits.

AIt is a well-known fact that radio-frequency amplifiers of thev so-called tuned radio-frequency type, wherein the tuning circuits constitute parts of a grid circuit, are subJect to 10 feedback currents, which currents, especially in multi-stage amplifiers, produce undesirable oscillations. Said oscillations combine with and distort the incomingsign'als, and, owing to regeneration, produce noisesxand sometimes the incoming signal is entirely wiped out.

These undesirable effects in existing circuits are chiefly due to the capacity effect between twol electrodes of the commonly used threeelectrode tube, wherein the plate 'circuits feed back currents to the grid circuits. In the multi-stage amplifier, in addition, stray fields between the transformers and alsol electrostatic fields betweenT condensers, increase the magnitude of undesired oscillations.

' The invention has for its object the production of a new tunin device and circuits therefor, whereby'undesirable oscillationsvin radiofrequency circuits are avoided.

Another object of this invention is to elimi-A nate so-called body capacit'yeiects, which are I noticeablein radio receivers using.

especially non-grounded loop antennae.

The invention will bebetter understood by!` referring to the attached drawings, in

whi Y 1 Figure 1 is a circuit diagram showing the invention as appliedto one stage of radio amplification Figure 2 shows a modification of the ,invention, and

Figure 3 shows the modification appearing in Figure 2, in an apparatus having multi stage circuits. y

VIn Figure 1 is shown a tuning` circuit comprising an inductive coil 1 and variable capacity 2. The circuit is tuned in accordance with the incoming frequency, and the coil 1 receives energy from an outside` source such as a broadcasting station or a coil 12, assuming that coil 1 is inductively coupled tocoil 12.

At any given instant the condenser 2 is charged so that a difference of potential V between its two electrodes, 3 and 4, is equal to the difference of potential generated on the coil 1, and, if the lower plate 4 is grounded and has a consequent zero potential, as shown .by dotted ground line 5a the upper plate 3 will have a vpotential V.

Between the two plate-electrodes of the condenser a third electrode 6 is interposed. This electrode may be a fine mesh of wire of any conductive substance, or a perforated plate of total potential difference is:

+v1- vz) :V One potential factor, l-fvl, is applied to the grid circuit of the tube by connecting the grid electrode 7 to upper plate 3 and the filament 8 to the third elect-rode 6, while the other potential factor, '02, is-applied to the plate electrode 9 of the tube through a small adjustable condenser' 10, thus establishing a tuned circuit which is adapted to react upon both the grid and theplate circuit of'ajthree-electrode tube. vThe capacity of condenser 10 can be so ad-` justd that' it will satisfy the equation QP Yi Cp V2 where'Cbis 'the capacity value of condenser 10, ,CD capacity between plate and-grid,`and "v1, v2 'are the values' previously defined.l In this case, feedback currents originating in .the plate circuit 11 will leak between elements 9 and 7 to the upper plate 3, and through the condenser 10 to the lower plate/4 and return by the electrostatic screen 6 to filament 8, thereby establishin a potential difference between each plate of condenser 2 and the electi'ostatic screen of such magnitude that V1D+V2D=Oi i* e', V19: Vzm'where Viv and Vm, are, respectively, voltage drops' due to plate feedback currents.

It is evident that, if the main tuning condenser is not affected by potential variations due to feedback currents, the winding atif grounded, as shown y It is a known fact that the electrostatic fieldY established between the two lates of a condenser is partly dissipated an radiated therei I claim'is:

from, producing so-called radiation losses. When, however, an electrostatic shield is used, the radiation'field will affect the electrostatic shield, and, by induction and on account of zero-shield potential, change the distribution of potential on the condenser plates in the same manner as the electrostatic screen placed in the middle of the condenser.

In Figure 2, parts 1 to 10, inclusive, are identical with the elements designated by the same indices in Figure 1. However, for the electrostatic screen is substituted a grounded electrost-aticshield 13. 'This shield 18 is insulated from the variable capacity 2, and, because of its relation to said variable capacity, will change the distribution of the potential `011 the plates 3 and 4, in the same manner as ythe electrostatic screen 6, shown in Figure 1.

Figure 3 shows a multi-stage set, in which a shield, such as is shown in Fi ure 2, is employed in each of it-s stages of ra io frequency. t should be noted that for proper operation of this set the polarities of two adjacent windings, 11 and'14, of a transformer 15, should be reversed.

n The electrostatic shield, being grounded or of zero potential, does not affect tuning of the elements of the circuit, and theapproach of an operators hand to the receiver will not affeet such turning because the operators potential is substantially the same as that of said shield. This fact is of special value if a loop receiver having no ground connection is used, since the approach of an operators capacity introduces no additional aerial to the circuit. In fact, in the type of circuit just described, the electrostatic shield can be actually grounded to the earth without impairing the directional qualities of the loop reception.

The drawings further show, antenn 16, filament batter 17 with its regulating resistance 18 anniI plate battery 19, necessary for the operation of the circuit. It will be understood that when a loop antennae is preferred the connection to the actual ground is not essentialras the Inetalwfrarneofv the apparatus will serve as a ground v Having thus described my invention, what 1. A radio apparatus provided with an oscillatory circuit including a condenser, and

an element electrostatically associated with said condenser, two of the condenser plates and said element being connected with the control electrode, the anode and the cathode of the ra dio-amplifying tube, and means to regulate feed-back currents in said circuit.

2. A radio-frequency amplifier including a thermionic tube, an oscillatory circuit comprising a coil and a condenser, and a grounded clement electrostatically coupled to said condenser, said element being connected to the cathode of said tube, and the pla-tes of said condenser beingy connected to the grid and plate of said tube.

A radio circuit including a thermionic tube, a condenser having associated therewith electrostatic means comprising an element electrostatically related to plates of said condenser, and another adjustable element, said elements being employed for balancing feedback currents in the said circuit.

4. A radio apparatus including an oscillatory circuit comprising an induction coil and a condenser, an electrostatic element surrounding and insulated from said condensers elements, and constituting a third element of said condenser, a thermionic tube, two electrical connections from two elements of the condenser leading to the cont-rol and anode electrodes of said tube, means for regulating the flow of current in one of said connections, and a connection between the third element and the cathode.

5. A neutralizing system including an oscillatory circuit having therein the secondary of a transformer and a condenser, and an element electrostatically associated with said condenser, a thermionic tube, a grounded connection between said element and the cathode of said tube, and an adjustable connect-ion between one plate of the condenser `and the anode of the tube, the other plate of the condenser being connected to a grid of said tube.

6. In an electrical circuit having as an input circuit for a thermionic tube the secondary of a transformer and a variable condenser, an element electrostatically associated with -said condenser producing a potential intermediate of potentials generated on said Variable condenser and connected to the cathode of said thermionic tube, said condenser being connected to the input and anode circuits of the tube.

7 A radio apparatus including an oscillatory circuit, athermionic tube having a cathode, a grid and a plate, one plate of the condenser in said oscillatory circuit being connted with the grid-elect-rode and the other plate thereof being connected with the plateelectrode'of. said tube throughan adjustable condenser, and a 'groundedelement electrostatically' associated with, surrounding and insulated from said condenser and connected with the cathode` of said tube. j

8'. A radio apparatus including a tuning circuit having therein a condenser and an associated element electrostaticall related to said condenser, a thermionic tu electrical connections from said element and one plate of the condenser adapted to react on the grid circuit of the tube, and electrical connections from said element and another plate of the,

condenser including an adjustable condenser in the plate lead adapted to react on the plate circuit of said tube. f y

9. A radio-frequenc amplifying apparatus including a tune circuit comprising a coil and a condenser, a thermionic tube, a plate circuit comprisin the primary winding of a transformer, an means to neutralize grid and plate capacity eifects producing yundesirable reactions between the grid and the plate circuits, said means comprising an electrode electrostatically associated with said condenser and connected to a cathode of said tube, and an electrical connection between a plate of the condenser and the plate of said tube including an adjustable capacity to regulate ow of current from the plate circuit to the grid circuit of said tube.

10. A radioapparatus including a thermionic relay, input and output windings associated with the control electrode and the an ode of said relay, a condenser across one of said windings, an electrostatic element inductive-ly related to said condenser and connected to the cathode of said relay, and adjustable means to balance undesirable feed-back curlrents due to inter-electrode capacity of said relay.

11. A radio ap aratus including an oscillatory circuit, a t ree-electrode tube having the usual filament, grid and plate, one plate statically associated with and insulated from said condenserand connected with the lila ment of said tube, Y

12. A radio apparatus including a tuning circuit, a three-electrode tube having the usual filament, grid and plate, one plate of the.

condenser` in said tuning circuit being. connected with the gridelectrode and the other plate thereof being connected with the plate v electrode of said tube through an adjustable condenser, and a third element associated with and insulated from said-condenser and connected with the ilament of said tube.

In testimon whereof I aliix my signature.

WLA IMIR J. POLYDOROFF. 

